Most commercially available and widely known low-pressure fluorescent discharge lamps are known as fluorescent lamps (FLs). Recently, compact fluorescent lamps (CFLs) have been designed to replace conventional incandescent lamps in a wide range of home and commercial applications. FLs and CFLs advantageously have lower power consumption and longer life properties as compared to incandescent lamps. In order to provide CFLs that resemble conventional incandescent lamps, a bulb shaped outer envelope may be provided that encapsulates the CFLs. The advantages of these CFL lamps are low power consumption and long lifetime. However, one of the main disadvantages of FLs, including CFLs, is their relatively long run-up time.
As mentioned above, a disadvantage of FLs and CFLs is their relatively long run-up time. Run-Up time may be defined as the time between the application of power to the FL or CFL and the time when the light output first reaches a specified percentage (usually 80%) of stable light output. In general, consumers expect a lamp to emit light immediately after, or substantially instantaneously with, the flipping of a switch to the ON position. However, some long-life FLs need about 0.5 to 1.5 seconds to preheat the cathodes or electrodes before starting to emit any light output. Thus, the FL emits no light before preheating is complete. In addition, in some cases once an arc discharge is initiated, an FL still requires an additional 20 seconds to fifteen (15) minutes or more to reach a certain percentage of its stabilized luminous flux or stable light output. Thus, the time for an FL to reach a predetermined percentage of its stabilized luminous flux can vary in a wide range.
Prior attempts to reduce the run-up time of a FL utilizing an amalgam mercury dose incorporated an auxiliary amalgam near one of the electrodes in the lamp. Since this arrangement results in the mercury from the auxiliary amalgam being vaporized shortly after the FL is switched ON, the run-up period is reduced. However, an instant light feature is not provided.
Another known solution combines a FL and an incandescent lamp in one unit. A suggested procedure involves simultaneously turning on the incandescent lamp and the FL when power is applied so that instant light (from the incandescent lamp) is provided, and then to subsequently switch OFF the incandescent lamp when the FL reaches a stable light output. But such a solution is inefficient and does not provide an effective manner for warming up the mercury source of the FL.
Yet another known solution is to apply power to only the incandescent lamp portion of a combined incandescent-FL unit when the lamp assembly is turned ON, and then once a predetermined temperature is reached, turn OFF the incandescent lamp and turn ON the FL. Although a thermal switch of such an arrangement aids in starting the FL in a low temperature, ambient condition, such an arrangement and method does not improve the run-up time of the lamp assembly.
External heating methods have also been attempted in order to reduce run-up times. In particular, one method involved painting a non-transparent metallic element, such as silver chloride paint, onto the outer surface of the glass tube of an FL to improve heating. However, using such a metallic coating results in a high loss of total lumen output of the lamp. In another method, a transparent resistive metallic layer such as fluorine doped tin-oxide (FTO) was applied onto the outer surface of the glass tube of a FL. But even in this case a shading effect occurs, which limits the light output.
Thus, a need exists for a method and/or apparatus for improving the warm-up or run-up time of a FL that overcomes the problems described above.